Synthesis of PAM and Na-Ac/AM Hydrogel-Coated Mesh for Separation of Oil/Water Mixtures

Abstract

Hydrogels are used in many applications and have gained popularity due to their high water content, good biocompatibility and similarity to soft tissue. The research objective is to design and synthesize self-healing hydrogels in water/oil/gas system targeted for the separation of water from oil-water mixtures. This will be achieved by graft polymerization of water-soluble polymer such as polyacrylamide (PAM) homo-polymer and poly (Na-Ac/AM) copolymer reinforcing on a thin-fine metallic mesh. This work also involves the study of the effect of mesh size on the amount of water recovered from the oil-water mixture. Further, the factors affecting the micro porosity of synthesized hydrogels such as swelling index are investigated. The hydrogel coated percentage and swelling index (a characteristic property of hydrogels that indicates how much water is absorbed by the gel) are investigated. Different experiments are performed using several mesh sizes and various industrial oils. The hydrogel morphology was analysed by using scanning electron microscopy. Experiments conducted provide quantitative data regarding the degree of the separation of oil from water by using hydrogels. PAM Hydrogel- Coated Mesh was fabricated using a photo-initiated polymerization process with acrylamide (AM), N, N’-methylene bisacrylamide (BIS), 2,2’-diethoxyacetophenone (DEOP), and polyacrylamide (PAM) (number average molecular weight is M_n= 5,000,000-6,000,000) as the precursor, cross-linker, initiator and adhesive agent, respectively. Distilled water was used to dissolve the AM, BIS, DEOP and PAM (50,55,60:1.5:1:0.5 by weight) respectively. Furthermore, Poly (Na-Ac/AM) Hydrogel-Coated Mesh was fabricated also by a photo-initiated polymerization process with sodium acrylate (Na-Ac), acrylamide (AM), N, N’-methylene bisacrylamide (BIS), 2,2’-diethoxyacetophenone (DEOP), and polyacrylamide (PAM), as co-monomer, precursor, cross-linker, initiator and adhesive agent, respectively. In these copolymer hydrogels, distilled water was used to dissolve the Na-Ac, AM, BIS, DEOP and PAM (10,55,50,5:1.5:1:0.5 by weight) respectively. The effect of the copolymer concentration on the separation time was studied through changing the monomers and the water concentrations. Oil-water mixtures of 5/95, 10/90 and 30/70 Oil/Water % were chosen based on industrial practices as it is not typical to find a wastewater stream with more than 30% oil composition. In all cases, water passes through the mesh, whereas the oil remained in the upper glass tube. Any remnant oil that existed in the permeated water inside the beaker was analysed with an oil analyser. The wettability of water and oil on the PAM- hydrogel coated mesh was evaluated using the contact angle measurements obtained at ambient temperature. It was found that PAM polymer and Na-Ac/AM copolymer hydrogel coated meshes is a super-hydrophilic in an air-solid-liquid three phases with both the contact angle of oil and water lower than 15 degree and in under-water membrane become highly repulsive for oil, where all underwater OCAs of the four different size of meshes based on PAM coated mesh are greater than 90 degree. This indicates the hydrophobic properties of the coated mesh under the water and oil cannot penetrate through the coated mesh while the water absorbed through it. The difference in the water flow or separation time becomes smaller with increasing the mesh’s pore size up to 80 micron, while separation time was higher for 200 micron mesh as more hydrogel was as hydrogel was blocking the pores. In contrast, the separation time is faster with the copolymer due to the higher swelling capacity of the copolymer. Therefore, under-water oleo-phobic properties of the PAM coated mesh make it a promising candidate for many applications, such as for wastewater treatment produced in industry and daily life with more than 95% separation efficiency. However, Na-Ac/AM copolymers coated meshes have lower separation efficiency than PAM homo-polymer due the highest swelling capacity of copolymers hydrogels, which end up with taking off from the mesh.